Flame supervision devices for burners



Nov. 1, 1966 F. L. F. STE GHART ETAL FLAME SUPERVISION DEVICES FOR BURNERS Filed July 15, 1965 FIG.2.

FIGS.

United States Patent 3,282,322 FLAME SUPERVISION DEVICES FUR BURNERS Fritz Ludwig Felix Steghart, Gerrards Cross, and Peter Leslie Kershaw, Slough, England, assignors to Satchwell Controls, Ltd., Slough, Buckinghamshire, England, a corporation of Great Britain Filed July 13, 1965, Ser. No. 471,675 Claims priority, application Great Britain, July 24, 1964, 29,767 64 7 Claims. (Cl. 15828) This invention relates to a device and method for flame supervision for burners which are for use primarily with central heating systems.

Flame supervision devices necessarily comprise a flame detecting means which may be responsive to visible, infra-red or ultra-violet light. Flame detecting devices responsive to visible light have the disadvantage that they cannot be used with certain types of gas flame, for example, because the gas flame may not produce enough light to affect such a flame detecting device. Flame detecting devices responsive to infra-red light have the disadvantage that they may be affected by heat from a furnace chamber even though flame has become extinguished. A flame detecting device responsive to ultraviolet light is therefore to be preferred.

Flame detecting devices responsive toultra-violet light may, in the course of time, change their characteristics in such a way that their operation becomes abnormal and potentially dangerous. Such a device generally comprises a photo-emissive surface enclosed in a quartz glass envelope. The abnormal operation is usually due to cracks developing in the envelope, these cracks permitting air to enter and cause the flame detecting device to act as if ultra-violet light were falling upon it even though this is not so.

An object of the invention is to provide a flame supervision device which prevents such abnormal operation becoming dangerous and prevents a short circuit or open circuit of any element or a malfunctioning of the device simulating the existence of flame, after proving the circuit initially when heat is required.

Conventional flame supervision devices are generally so arranged that if flame is not established within a certain period the device assumes a lock-out condition in which means for supplying fuel to the burner and means for igniting such fuel are both rendered inoperative until the flame supervision device is manually reset.

According to the invention, a flame supervision device comprises two detectors each for providing an electrical signal when exposed to radiation from the flame, a first relay responsive to the signal from at least one of the detectors when flame is present to prevent interruption of supply of fuel, and a second relay responsive to a difference between the signals from the two detectors departing from a predetermined value to cause the device to interrupt the supply of fuel. Preferably, said first relay is responsive to the sum of the signals from the two detectors.

Preferably also the flame supervision device comprises two normally-equal photo cells for detecting flame, the first relay being responsive to the sum 'of the currents flowing through the two photo cells when flame is present to prevent the device assuming a lock-out condition and said second relay being responsive to a predetermined difference between said currents to cause the device to assume a lock-out condition.

By arranging that the second relay is responsive to a difference between the currents flowing through two norma'lly equal photo cells it is possible to detect when one of the photo cells operates abnormally and, when that ice happens, to cause the device to assume a safe (lock-out) condition almost immediately.

Preferably, in order to reduce the power required to operate the first relay, the first relay is provided with a single normally-closed switch in a first energising circuit for the second relay, the first energising circuit being completed when heat and thus flame is required; the second relay is provided with a single normally-open switch which closes when the first energising circuit is broken or when the photo cells pass currents which differ by more than said predetermined value, the closing of the normally-open switch causing the device to assume the lockout condition.

The relays may be of the electro-mechanical type but they may, alternatively, be of any suitable electronic or semi-conductor type.

The invention also comprises a method of burner flame supervision in which two detectors are employed to detect radiation from thte flame, a signal from at least one of the two detectors is employed to determine when flame is present, and signals from the two detectors are compared to indicate the functional condition of the detectors.

Preferably, the method includes the step of interrupting fuel supply to the burner if the sum of the detector signals fall below a determined value or the difference between detect-or signals depart for .a predetermined value.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings in which:

FIG. 1 is a partly-schematic circuit diagram; and

FIGS. '2 and 3 show, schematically, two alternative arrangements of a probe head.

Referring to FIG. 1, the flame supervision device comprises essentially a first flame relay FRI, a second flame relay FRZ, a first thermal delay device FD and a second thermal delay device SD.

The first flame relay FRl comprises a movable contact arm 1, a fixed contact 2 and a coil 3. Contact arm 1 is normally closed on contact 2 and suitable energisation of the coil 3 causes it to break from contact 2. The conditions under which this occurs will be described below.

The second flame relay PR2 comprises a contact arm 4 which is normally open from a fixed contact 5, a first coil 6 and a second coil 7 having a centre tap.

The first delay device FD comprises a bi-metallic strip 13 exposed to heat from heaters 15 and 16 and operatively connected to contact arms 17 and 19 so that these contact arms make with fixed contacts 18 and 20 respectively when the bi-metallic strip 13 is hot and breaks from the fixed contacts 18 and 20 respectively when the bi-metallic strip is cool.

The second delay device SD comprises a bi-metallic strip 21 exposed to heat from heater 22 and operatively connected to contact arm 23 so that contact arm 23 makes with fixed contact 24 when the bi-metallic strip 21 is cold and makes with a fixed contact 25 when the bimetallic strip 21 is hot.

Manual resetting of contact arm 23 is necessary to cause it to break from contact 25 and remake with contact 24.

The first flame relay FRI, the second flame relay PR2, the first delay device FD andthe second delay device SD are housed in a common housing FSD provided with terminals L and N for connection to a single phase power source. The housing FSD is also provided with a warning lamp 26 the function of which will be described below. A transformer 11 for energising the windings 3 and 7 is also provided Within the housing FSD.

The flame supervision device also comprises certain elements located outside the housing FSD. These are:

(1) A thermostat T which closes to indicate that heat is required;

(2) An ignition transformer I which, when fully energised, causes high voltage sparks to pass between ignition electrodes in a furnace chamber;

(3) The photo-emissive cells 8 and 10 are centre tapped resistor 9 located in a probe head positioned near the furnace chamber so that the cells 8 and 10 are exposed to ultra-violet light from flame in the furnace chamber; and,

(4) A motor or valve M which, when energised, causes fuel to be supplied to a burner located in the furnace chamber.

Circuit connections between the elements referred to above will be apparent from inspection of the drawing.

When thermostat T closes to indicate that heat is required the flame supervision device normally passes through the following conditions in sequence.

During a pre-ignition period Commencing with the closing of the thermostat T and ending with the operation of contact arms 17 and 19:

(a) An energising circuit for the second flame relay PR2 is completed, this energising circuit extending from terminal L through contact arm 23, contact 24, thermostat T, contact arm 1, contact 2, winding 6 and terminal N. The contact arm 4 therefore closes on contact 5.

(b) An energising circuit for ignition transformer I is completed, this energising circuit extending from terminal L through contact arm 23, contact 24, thermostat T, ignition transformer I, contact 5, contact arm 4 and terminal N. The ignition transformer T is therefore fully energised and high voltage sparks pass between the ignition electrodes for a period long enough to clear away deposits from these electrodes.

(c) An energising circuit for heater 15 of the first delay device FD is completed, this energising circuit extending from terminal L through contact arm" 23, contact 24, thermostat T and heater 15 to terminal N.

(d) An energising circuit is completed for heater 16 of the first delay device PD and heater 22 of the second delay device SD, these heaters being connected in series. This energising circuit extends from terminal L through contact arm 23, contact 24, thermostat T, heater 16, heater 22, contact and contact arm 4 to terminal N.

As a result of the heaters 16 and 22 being connected in series, the current passing through heater 22 is insufficient to cause contact arm 23 to break from contact 24 and make with contact 25. The resultant slight heating of the bi-metallic strip 22 is, however, sufficient to render the second delay device capable of rapid operation when heater 22, contact 5 and contact arm 4 to terminal N.

(e) An energising circuit for coil 7 of the second flame relay PR2 is completed, this energising circuit extending from terminal L through contact arm 23, contact 24, thermostat T, primary winding 12a of transformer 11 to terminal N, the energisation of primary winding 12a inducing a voltage in secondary winding 12b of transformer 11. The secondary winding 1% is connected in series with winding 3 between centre taps on winding 7 and resistor 9. When the photo cells 8 and 111 operate normally they pass equal currents under the influence of the voltage induced in the secondary winding 12b, these equal currents flowing in the respective halves of the winding 7 and exerting equal and opposite effects on contact arm 4 so that contact arm 4 remains closed on contact 5.

At the end of the pre-ignition period (f) Warping of the bi-metallic strip 13 due to the energisation, referred to under (b) and (c) above, of heaters 15 and 16 causes contact arms 17 and 19 to close on contacts 18and 21 respectively.

(g) Closing of contact arms 17 and 19 on contacts 18 and 20 respectively completes an obvious energising circuit for the motor or valve M, this energising circuit extending from terminal L to terminal N and including contact arms 17 and 19 and contacts 18 and 20. Energisation of motor or valve M causes fuel to be supplied to the burner and, as the ignition transformer T is already energised, ignition of the burner normally occurs after a short delay.

(h) Closing of contact arm 19 on contact 20 short circuits heater 16. The continued energisation of heater 15 is suflicient to maintain contact arms 17 and 19 in contact with contacts 18 and 20 respectively although the energisation of heater 1'5 alone is suflicient to operate contact arms 17 and 19.

(i) The closing arm 19 on contact 20 completes a second energising circuit for heater 22 to fully energise the heater 22, this energising circuit extending from terminal L through contact arm 23, contact 24, thermostat T, contact 20, contact arm 19, heater '22, contact 5 and contact arm 4 to terminal N. If this full energisation of heater 22 continues for a period known as the lock-out period, the bi-metallic strip 21 warps and causes contact arm 23 to break from contact 24 and make with contact 25.

Before the end of the lock-out period (j) If the fuel is ignited, ultra-violet light from the flame falls on the photo cells 8 and 10 which, if they operate normally, pass sufficient current through winding 3 to the cause contact arm 1 to break from contact 2.

(k) The breaking of contact arm 1 from contact 2 opens the second energising circuit for heater 22 referred to at (i) above, with the result that contact arm 23 remains in contact with contact 24. The motor or valve M therefore continues to be energised until thermostat T opens.

(l) The breaking of contact arm 1 from contact 2 opens the energising circuit for the ignition transformer T referred to at (b) above with the result that the three heaters 15, 16 and 22 are inserted in series with the ignition transformer T. The ignition transformer is then insufficiently energised to provide sparks. As a result of the operations (j), (k) and (1) the fuel is ignited and continues to be supplied until thermostat T opens, the ignition transformer having ceased to supply sparks. This is the normal running condition of the flame supervision device.

At the end of the lock-out period (m) If flame is not established, no light falls on the photo cells 8 and 10 and the current flowing through winding 3 is insuflicient to 'break contact arm 1 from contact 2.

(n) The continued closure of contact arm 1 on contact 2 ensures that the heating of the bi-metallic strip 21 due to the continuous full energisation of heater 22 causes contact arm 23 to break fromcontact 24 and make with contact 28.

(o) The breaking of contact arm 23 from contact 24 opens the energising circuit for the ignition transformer T referred to at (b) above and the energising circuit or motor or valve M referred to at (g) above. The burner therefore shuts down and cannot be restarted until contact arm 23 is manuallly reset to its original position.

(p) The making of cont-act arm 23 with contact 25 completes an obvious energising circuit for warning lamp 26 which therefore lights to indicate the device has assumed a lock-out condition and needs to be manually reset before further operation is possible.

Effect of unbalance between the currents passed by the photo cells due to cracking of envelope, for example (a) Before flame is established:

As only the faulty photo cell will pass current the current passing through winding 3 cannot be sufficient to open contact arm 1 from contact 2. Winding 6 is therefore energised to cause contact arm 4 to close on contact 5 and heater 22 is fully energised at the end of the preignition period to cause the device to assume a lock-out condition at the end of the lock-out period.

(b) After flame is established:

Before the unbalanced condition arises, winding 3 will be energised to open contact arm 1 and contact 2 and contact arm 4 will be open from contact 5. Upon the development of the unbalanced condition the currents flowing in the two halves of winding 7 become sufiicient- 1y unequal to cause contact arm 4 to close on contact '5, causing the flame supervision device to assume a lock-out condition.

FIG. 2 shows one arrangement of probe head comprising a housing 27 enclosing two separate photo cells 28 positioned within the housing to receive light from flame 29 through a tubular portion 30 of the housing. The tubular portion is cylindrical and may contain a lens 31 for directing radiation onto the photo cells.

FIG. 3 shows an alternative arrangement in which the tubular portion 30 is of conical form and the proportion of radiation falling on the two photo cells is adjustable 'by rotation of a prism 32 which is transparent to radiation from the flame.

The two flame relay-s are described above as being of the electro-mechanical type. They may, alternatively, be replaced by solid-state circuitry including transistor elernents.

We claim:

1. A flame supervision device for a burner, the device comprising two detectors each adapted to provide an electrical signal when exposed to radiation from the flame, a first relay means adapted to respond to the signal from at least one of the detectors when flame is present to prevent interruption of supply of fuel to the burner, and a second relay means adapted to respond to a difierence between the signals from the two detectors departing from a predetermined value to cause the device to interrupt the supply of fuel.

2. A flame supervision device according to claim 1, in which said first relay means is adapted to respond to the sum of the signals from the two detectors.

3. A flame supervision device according to claim 2, and comprising two normally-equal photo cells for detecting flame, said first relay means being adapted to respond to the sum of the currents flowing through the two photo cells when flame is present to prevent the device assuming a lock-out condition, and said second relay means being adapted to respond to a predetermined difierence between said currents to cause the device to assume a lockout condition.

' 4. A flame supervision device according to claim 3, and comprising an energising circuit for said second relay means and which is completed when flame is required, a normally-closed switch in said circuit and operated by said first relay means, and a normally-open switch operated by said second relay means to close on occurrence of one of the following conditions which are that said energising circuit is broken and that said photo cells pass currents which difier by more than said predetermined value, the closing of said normally-open switch being adapted to cause the device to assume a lock-out condition.

5. A flame supervision device according to claim 1, in which said relay means include electro-mechanical relays.

6. A method of burner flame supervision, comprising employing two detectors to detect radiation from the flame, employing a signal from at least one of said two detectors to determine when flame is present, comparing signals from the two detectors to indicate the functional condition of the detectors and interrupting fuel supply to the burner if a sum of the detector signals falls below a predetermined value.

7. A method of burner flame supervision, comprisin'g and employing two detectors to detect radiation from the flame, employing a signal from at least one of said two detectors to determine when flame is present, comparing signals from the two detectors to indicate the functional condition of the detectors and interrupting fuel supplied to the burner if a difference between the detector signals departs from a predetermined value.

References Cited by the Examiner- FOREIGN PATENTS 1,211,844 3/1960 France. 1,233,672 10/1960 France.

JAMES W. WESTHAVER, Primary Examiner. 

1. A FLAME SUPERVISION DEVICE FOR A BURNER, THE DEVICE COMPRISING TWO DETECTORS EACH ADAPTED TO PROVIDE AN ELECTRICAL SIGNAL WHEN EXPOSED TO RADIATION FROM THE FLAME A FIRST RELAY MEANS ADAPTED TO RESPOND TO THE SIGNAL FROM AT LEAST ONE OF THE DETECTORS WHEN FLAME IS PRESENT TO PREVENT INTERRUPTION OF SUPPLY OF FUEL TO THE BURNER, AND A SECOND RELAY MEANS ADAPTED TO RESPOND TO A DIFFERENCE BETWEEN THE SIGNALS FROM THE TWO DETECTORS DEPARTING FROM A PREDETERMINED VALUE TO CAUSE THE DEVICE TO INTERRUPT THE SUPPLY OF FUEL. 